Breastpumps for use by nursing mothers are well known. They allow the nursing woman to express the breastmilk as necessary or convenient, and further provide collection of the breastmilk for later use. For some mothers, breastpumps may be a necessity, such as when the child has suckling problems, or if the mother has problems with excessive or deficient milk production, or soreness, deformation or injury of the mammilla, or like conditions that are not conducive to suckling at the breast.
There are three general broad classifications of breastpumps: hand pumps that generate suction manually, battery operated pumps with small motors that generate suction from power supplied by batteries, and electric pumps in which suction is created by various types of electric motors that run off “house” current. Some pumps can cross over these broad classifications.
Various types of hand pumps exist. An example of such manually-driven pumps is in U.S. Pat. No. 6,497,677.
A battery-driven portable breastpump is described in U.S. Pat. No. 4,964,851, for example. This breastpump is small, lightweight and achieves good vacuum (i.e., negative pressure) regulation in preferred limits. The LACTINA breastpump sold by Medela, Inc. is also another type of breastpump, which may be driven by battery as well as house current. It is generally disclosed in U.S. Pat. No. 5,007,899.
All of these breastpumps are designed to cycle pressure, typically a negative pressure or vacuum, that is applied to the breast and nipple within the breastshield. Conventional breastpumps are generally of the displacement pump type or accumulator pump type. Displacement pumps use a mechanism to expand a volume to thereby generate a vacuum, such as the foregoing piston-type pumps. At the end of the return stroke, they return to atmosphere. A maximum (or other) vacuum is achieved by the length of the stroke. Upon returning the breast shield to atmospheric pressure, a one way valve may be opened to discharge accumulated leakage air, excess air from the repositioning of the breast tissue, and expelled milk within the breast shield. The discharge occurs into an atmosphere vented milk collection bottle or flexible bag. Alternatively, air can be adjustably added during a fixed-length stroke (as by an adjustable return to atmosphere) to roughly establish a desired vacuum level.
Accumulator pumps build up vacuum by repeatedly exhausting small portions of the original quantity of gas in the system. As the amount of gas (air) in a fixed volume decreases, the pressure decreases causing the vacuum to increase. Accumulator pumps control the maximum vacuum via the time, or duration, the pump is powered on and operating, e.g., the number of pump reciprocations for a given cycle. Vacuum can also be adjusted via a regulator, like that of the battery-driven portable breastpump described in U.S. Pat. No. 4,964,851, for example.
An issue with conventional breastpumps is that the “system” volume within the breastshield varies due to the amount of volume the breast of a nursing mother occupies in the breastshield, as well as the response of a given breast under vacuum. For example, a nursing mother with engorged breasts will have tight breast and nipple tissue that may occupy the breastshield differently from a mother with highly elastic breast tissue and/or nipples. So too, a small breast or nipple may fill the breastshield and react differently from a large breast or nipple. The system volume thus varies from breast to breast, and even from time to time for the same breast.
This “variable system volume,” sometimes referred to as the “dead” volume, is problematic within a suction cycle. Imagine a highly elastic breast/nipple; at the start of the suction cycle, the breast and nipple occupy a certain portion of the breastshield system volume. This fixes the starting quantity of air in the system. As suction builds, the breast/nipple tissue is drawn into the breastshield, partially relieving the buildup of vacuum. Thus, the developed vacuum within the cycle is less than would be realized with a less elastic breast/nipple.
To the extent that conventional breastpumps of the displacement or accumulator types have attempted to provide actual set points for vacuum desired, they do so only through an approximation. A vacuum setting of “250 mmHg” for such pumps would only be for a standard sized breast for example, since it is based upon an expected level derived from displacement, or alternatively accumulation, effected by operation. The method or mechanism by which a vacuum is regulated is thus not controlled by the actual pressure sensed at the breast.
Some prior art patents disclose regulating pressure with a sensed pressure. U.S. Pat. No. 5,902,267 to Medo discloses a regulator within a central vacuum system that applies the regulated output to a pump “flange” on the breast, and then returns to ambient pressure in a cycle.
U.S. Pat. No. 6,383,163 to Kelly discloses a vacuum sensor for sensing suction in the breast cup and opening a valve when a maximum suction is sensed to release the pressure and return the breast cup to ambient. Upon the breast cup achieving ambient pressure, the valve closes for another cycle.
Unlike the present invention, the prior art does not regulate vacuum at the breastshield to reach a maximum negative pressure, and then a desired minimum negative pressure still less than ambient, without the need to return to atmospheric pressure for successful milk expression. A return to ambient pressure within the breastshield chamber may not be required, and benefits may be achieved by maintaining a minimum level of vacuum on the breast throughout at least a portion of the pumping session. Such would include, for example, reducing the amount of energy required to thereafter reach maximum vacuum. The “elastic rebound” of the nipple upon release of vacuum would also be minimized. Further benefits may result from being able to control a given vacuum cycle between desired set points of actually sensed, and thereby actually applied pressures, which set points may be made numerous for more complex, yet precisely controlled suction curves. The present invention also provides comfort to the nursing mother in that the reciprocation of a breast or nipple within the breastshield is minimized.
Patent application Ser. No. 11/786,364 entitled “Method and Apparatus for Minimum Negative Pressure Control, Particularly for Breastpump with Breastshield Pressure Control System,” describes means of using an accumulator breast pump with sensors to control the vacuum cycle precisely including the minimum vacuum. The application describes a breast shield which, when in contact with a breast, has internal pressure controlled by the control system, and where the internal breast shield pressure communicates with the milk collection bottle to bring the bottle to the minimum vacuum. Some slight cyclic variation to greater vacuum occurs each pumping cycle within the bottle collection. The collection bottle is sealed from the atmosphere. Opening of the one way valve is assisted by the higher vacuum in the bottle as the breast shield approaches the minimum vacuum, a lower vacuum.